Several new HLA-B locus alleles have been discovered in South American Amerindians. By contrast, analysis of the MHC class I alleles of North American native populations has revealed few new HLA-B alleles. This suggests that the HLA-B locus is evolving rapidly in South American populations. We described the HLA-B locus alleles present in individuals from a Central American tribe, the Kuna of Panama. Using a sequence-based typing technique that separates alleles by denaturing gradient gel electrophoresis (DGGE) followed by direct sequencing, we determined the HLA-B alleles from eight Kunas. Two of the HLA-B alleles present in the Kuna have been previously described in other South American Amerindian populations; one allele has been characterized in a Mexican-American. OBJECTIVE: To determine new B locus alleles in Central America. RESULTS We characterized two new HLA-B alleles in the Kuna, HLA-B*3911 and HLA-B*5110. HLA-B*3911 differed from HLA-B*3905 by only a single nucleotide substitution in exon 3. This substitution resulted in an amino acid replacement of leucine by arginine at residue 156 in the alpha 2 domain. Such a change may affect the repertoire of peptides that are bound by this molecule. HLA-B*5110 differed significantly from other HLA-B*51 alleles in that it is the result of an unusually large intra-locus recombination event of minimally 216 nucleotides. This recombination results in an allele that is part HLA-B*51 and part HLA-B*40. Thus, more dramatic recombination events may also play a role in the rapid evolution of the HLA-B locus in Amerindians. KEY WORDS DGGE, HLA-B*3911, HLA-B*5110, Kuna Amerindians, sequence, typing